NASA’s Mars Exploration Rovers (MER), which have spent nearly double their scheduled mission time on Mars, still are performing well as they prepare to enter even more challenging territory, according to NASA. The Spirit and Opportunity rovers “are both still in very good health, but we’re approaching more aggressive terrain at both sites, which [is] going to require more planning and more thought,” Chris Voorhees, rover engineer at NASA’s Jet Propulsion Laboratory (JPL), said at a press conference June 25. The rovers also are getting less power as the days get shorter and their solar panels accumulate dust. The rovers landed on Mars in January.